This invention relates to golf clubs and particularly to the continual adjustment of their shaft flex to match the dynamic characteristics of a player on a given day which we will refer to as tuning the shaft This is accomplished by the addition of a rigid tubular insert with a compressible outer surface which provides enough friction and compressibility to hold it in place when inserted within a golf club shaft so as provide a method of adjusting the overall shaft flex by changing its penetration within the shaft. The penetration can be changed at any time although the rules governing competitive golf forbid making such changes during a round
It is the object of this invention to provide the means to tune the shaft of a dynamically swung golf club, but not a putter which require adjustments other than flex, to match a player's tempo over a range.
It is a further object of this invention to compensate for misalignment of the spine of a shaft or at least not to add to the detrimental effects of said misalignment.
Technical specifications commonly used to describe golf clubs include: total weight, swing weight, length, loft angle, lie angle, head size and weight, grip diameter, and shaft flex. But the proper selection of the latter is generally acknowledged to be most important when fitting clubs to a golfer. Moreover, recent studies have shown that it is very important for custom golf club fitters to find the optimum flex for each player for improved shot control and greater distance. But finding the optimum flex has perplexed most teachers, club fitters and golfers.
Three methods for finding the best flex before club assembly presently dominate the market for custom clubs. In the first fitting method, the player swings one dub several times and the average club head speed measured and a formula used to calculate the flex for the entire club set The second approach relies on matching one club or a set of clubs to a players favorite club. In the third method, a player hits several shots with each of many calibrated test clubs, finally selecting the best of the lot judged by one of several radar devices that measure several parameters. The best club then serves as a model for his entire set, which can be matched to it. But once the clubs are constructed after fitting by any method, only minor adjustments of swing weight are possible until another set is purchased, in many cases by the golfer's belief that a better fit is probable.
Many factors such as club head speed, swing time duration, and acceleration, effect the choice of optimum flex for each player. So while it is generally accepted that there is a best flex for every player, the best flex on one day will not be the best flex for all days, since weather temperature and muscle tone change over the seasons. This suggests that a method for altering the flex of a golf club after it is constructed, even if it was fitted accurately to the conditions on the fitting day, would be a tremendous benefit For example, many of the touring pros bring with more than one driver to tournaments, choosing the one that works best on the driving range the same day of each tournament round. One famous pro, preceding his US Open win, warmed up before the last round, and choose one driver to play with over his two others that were separated by only one seventh of a flex each. The present invention allows flex adjustments over an entire flex and would eliminate the need to carry multiple drivers.
More recently, several leading club manufacturers began offering drivers with two or three quick-connect shafts in an effort to find a better flex fit. While one shaft is bound to be better than another, they are nevertheless separated by a whole flex and would yield the best flex only by chance. This conclusion is supported by tests on hundreds of players and proved that at least twenty test clubs separated by one seventh of a flex, or 3 CPM, are required to cover the range of flexes that prove to be best for 95 percent of golfers. To cover the same range with quick-connect shafts, the manufacturers would need to provide same number of shafts, or 20 shafts, instead of only three, each separated by only one seventh of a flex or 3 CPM. The cost of this approach would be prohibitive. But here comes this invention to help bridge the fine adjustments of flexes between the coarser steps allowed by only a few quick-connect shafts, which would need to be separated by only one whole flex, at a much lower overall cost.
To understand why adjusting the shaft flex of a golf club is critical for good play, one must understand the role of the shaft which is to deliver the club head to the ball at the best attitude and phase angle of the various oscillations occurring in the Swing Plane, Toe Plane and Torque Axis. For the ball to be struck solidly, the sum of these angles must compensate for the errors in that player's swing path and timing.
For maximum energy transfer and therefore the longest shots, the center of gravity of the club head should strike the ball. But for straighter shots for a golfer with an average swing, it may be better for ball contact to occur slightly off-center to compensate for player-induced errors in the swing plane or torque deflection errors caused by club head and shaft characteristics. Although hard to fix in practice, player-induced errors are easy to identify using photography. Errors in directional control due to shaft oscillation phase angle are much more difficult to measure. Shaft flex oscillation in the Swing, Toe and Torque Planes are measured during player swings using strain gauges mechanically attached to the shaft and electrically connected to a computer, and the waveforms recorded. During a typical swing of slightly over one second duration, the shaft bends around 3 inches in all directions through 1.25 cycles of its flex frequency, in both the Swing and Toe Plane, both axes having the same flex frequency. The Torque Plane features an oscillation that is independent of the other two flex frequencies and is three to four times higher, 3.75 to 5 cycles, depending on the shaft model, with amplitude of a few degrees of angle. All three axes can have different phase angles at ball contact, varying from swing to swing for the same player, and varying more from player to player. The Toe Plane phase angle predominantly determines where on the club head the ball is struck, and the Swing Plane and Torque Plane phase angles determine the aiming direction of the club head at contact.
For example, if the club head is slightly open at ball contact due to player-induced Swing Plane error and Torque oscillation combined, which would cause the ball to go to the right of the target, then striking the ball off-center near the toe of the club face is best, since that will bring the ball back toward the target line. This is known as the gear effect due to right-to-left spin imparted from such contact, the latter of which being well known in the art. The net result of all these errors, without identifying the extent of any of them, is that some errors will cancel each other and cannot be predicted in their net effect, which is required to build optimized clubs with fixed parameters. The best compromise of each player's swing idiosyncrasies and club design parameters can only be found by adjusting the flex after club manufacture in order to adjust shaft deflection incrementally in the Toe Plane. This has the effect of determining where the ball strikes the club head, which the inventor believes allows fine tuning of directional control for most players. This concept runs counter to almost all that is written and most likely believed by experts who teach golf and design golf equipment, but is the crux of this invention. Most preferably, the adjustment of the flex of a club is performed after the club has been assembled as this technique provides an opportunity to compensate for all the variables in a practical manner